Network switching device

ABSTRACT

Network switching arrangements including: setting an operation mode of a target switching block to a operation mode that is different from an operation mode of a first switching block while the first switching block is handling a switching process, the target switching block being one switching block selected from second switching blocks; performing a switchover process including starting the switching process using the target switching block instead of the first switching block, after completion of setting the operation mode of the target switching block; and copying the switching information held by the first switching block to the target switching block, prior to starting the switching process using the target switching block, after completion of setting the operation mode of the target switching block.

CROSS REFERENCE TO RELATED APPLICATION

This is a continuation of U.S. application Ser. No. 13/149,029, filedMay 31, 2011, which is a continuation of U.S. application Ser. No.11/487,992, filed Jul. 18, 2006 (now U.S. Pat. No. 7,953,220). Thisapplication relates to and claims priority from Japanese PatentApplication No. 2006-049955, filed on Feb. 27, 2006. The entirety of thecontents and subject matter of all of the above is incorporated hereinby reference.

BACKGROUND

Technical Field

The present invention relates to network switching devices, and inparticular to reducing power consumption in network switching devices.

Description of the Related Art

A network switching device, including a switch and a router, is acritical device in a network system. In recent years there have beenremarkable increases in performance and capacity of the networkswitching device accompanying an increase in data traffic sent throughthe network and accompanying an increase in size of the network. On theother hand, accompanying the increased performance and the increasedcapacity there has also been a tendency for increased power consumptionin the network switching device as well, and controlling powerconsumption of the network switching device has become an issue fromboth the perspective of system operating costs and environmentalprotection.

Technologies that provide a normal mode and a low-power mode in devicesthat are connected together through a cable are known.

When mode is set in network switching device, problems may occur in theswitching process due to the mode setting (for example, the switchingprocess may be interrupted when the mode is being set), and there havebeen cases wherein this has resulted in extended interruption time ofthe switching process.

SUMMARY

An advantage of some aspects of the invention is to provide a technologythat is able to control power consumption while preventing theinterruption time of the switching process from becoming excessivelylong.

In an aspect of the present invention, there is provided a networkswitching device. The network switching device includes an interfaceblock, a first switching block, one or more second switching blocks, anda system control block. The interface block has a plurality of physicalinterface blocks. The physical interface blocks are configured toconnect to connection lines. The interface block is configured to sendand receive, through the lines, packets having associateddestination-address information. The first switching block is configuredto perform switching-determination process that determine a connectionline to which the received packets should be outputted, based on thedestination-address information that is associated with the receivedpackets. The second switching blocks are capable of performing theswitching-determination process instead of the first switching block.The system control block is configured to control the operation of eachof the blocks. The first switching block and the second switching blockare each provided with a plurality of switchable determination-operationmodes as operation modes for the switching-determination process. Theplurality of determination-operation modes includes a firstdetermination-operation mode and a second determination-operation modewith less power consumption than the first determination-operation mode.Furthermore, the system control block performs (A) a mode-processincluding setting the determination-operation mode of a target switchingblock to a determination-operation mode that is different from thedetermination-operation mode of the first switching block while thefirst switching block is handling the switching-determination process.The target switching block is one switching block selected from thesecond switching blocks. Furthermore, the system control block performs(B) a switchover process including starting the switching-determinationprocess using the target switching block instead of the first switchingblock, after completion of the process of setting thedetermination-operation mode of the target switching block.

Regarding this network switching device, the determination-operationmode of the target switching block is set to a determination-operationmode that is different from the operation mode of the first switchingblock during the period wherein the first switching block handles theswitching-determination process. Furthermore, theswitching-determination process is started by the target switchingblock, instead of the first switching block, after completion of settingthe operation mode of the target switching block. Thus, this networkswitching device makes it possible to changeover thedetermination-operation mode used for execution of theswitching-determination process without setting the operation mode ofthe switching block in execution of the switching-determination process,nor interrupting the switching-determination process.

Note that the present invention can be embodied in a variety of forms,for example, may be embodied in the form of a control method and devicefor a network switching device, a computer program for realizing thefunctions of such method or device, a recording medium on which suchcomputer program is recorded, a data signal that is incorporated into acarrier wave that includes such computer program, and so forth.

These and other objects, features, aspects, and advantages of thepresent invention will become more apparent from the following detaileddescription of the preferred embodiments with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a block diagram of the basic structure of a network devicepertaining to an embodiment;

FIG. 2 shows a block diagram of the internal structure of the systemmanagement block;

FIG. 3 shows a block diagram of the structure focusing on an interfaceboard and a switching board;

FIG. 4 shows an explanatory diagram of one part of the contents of asettings file;

FIG. 5 shows a flowchart of a processing routine in a startup process;

FIG. 6 shows an explanatory diagram for explaining the traffic loadbasis running mode and the periodic basis running mode;

FIG. 7 shows a flowchart of the processing routine in a frequencycontrol process in the traffic load basis running mode;

FIG. 8 shows a flowchart of a processing routine in a frequency controlprocess in the periodic basis running mode;

FIG. 9 shows a figure for explaining an auto negotiation function thatautomatically coordinates the line speeds/communications modes of a linebetween a pair of mutually-connected devices;

FIG. 10 shows a flowchart of a processing routine in a frequency controlprocess in the line speed basis running mode;

FIGS. 11-15 are schematic diagrams illustrating in greater detail theoperation mode management process;

FIGS. 16-20 are schematic diagrams illustrating an overview of aoperation mode management process;

FIGS. 21-25 are schematic diagrams illustrating an overview of theoperation mode management process;

FIG. 26 shows a block diagram of the structure of a network switchingdevice pertaining to a first variation; and

FIG. 27 shows a block diagram of the structure of a network switchingdevice pertaining to a second variation.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Embodiments of the invention will be described below in the followingorder.

-   A. First Embodiment-   B. Second Embodiment-   C. Third Embodiment-   D. Variations    A. First Embodiment    Structure of a Network Switching Device

The structure of a network switching device according to the embodimentwill be explained in reference to FIG. 1 through FIG. 3. FIG. 1 shows ablock diagram illustrating the basic structure of a network devicepertaining to the embodiment. FIG. 2 shows a block diagram of theinternal structure of a system management block. FIG. 3 shows a blockdiagram of the structure focusing on an interface board and a switchingboard.

As is shown in FIG. 1, the network switching device 1000 pertaining tothe embodiment includes, primarily, a control board 10, a switchingboard 100, and an interface board 300. The control board 10 includes asystem management block 11. The control board 10 is connected, so as tobe able to communicate, through a control bus 400 to the switching board100 and the interface board 300. The system management block 11 of thecontrol board 10 sends control signals to each of the constituentelements of the interface board 300 and the switching board 100, andreceives various type of information from each of these elements,through the control bus 400. In FIG. 1, two control boards 10 areprovided in order to improve reliability through redundancy, where oneis a active control board that is used at normal times, and the other isa standby control board that is used when a failure occurs in the activecontrol board.

The system management block 11 is a controller for controlling thenetwork switch 1000 as a whole. As shown in FIG. 2, the systemmanagement block 11 includes a central processing unit (CPU) 12 and amemory 13. The memory 13 stores a control program 14 and a settings file17. The CPU 12 executes the control program 14 to produce the functionsof the system management block. The control program 14 includes avariety of modules, such as modules that perform process relate torouting protocol such as RIP (routing information protocol) or OSPF(open shortest path first), etc., but only those structures required fordescribing the embodiment have been selected for inclusion in thefigure, and the detailed description of the invention describes thestructures that are shown. The control program 14 includes a trafficcheck module 15, a frequency control module 16, and a line speed checkmodule 18. The traffic check module 15 communicates with the switchingboard 100 to receive the traffic load for the packets that are processedby the switching board 100. A frequency control module 16 controls thesetting/changing of the operating frequency (the clock signal frequency)of the various types of buses (explained below) and circuits included inthe switching board 100 and the interface board 300. For example, in thestartup process described below, the operating frequency is setdepending on the operation mode. The line speed check module 18 checksthe line speed of each line 600 that are connected to the respectivephysical interface blocks 320. The processes performed by these moduleswill be described in greater detail below.

In the embodiment, the network switching device 1000 includes twoswitching boards 100. The two switching boards 100 each have identicalstructures, and in FIG. 1, identical constituent elements are givenidentical codes. Each switching board 100 includes a packet processingblock 120, and a routing control block 130. The packet processing block120 is connected by an internal bus 140 so as to be able to communicatewith the routing control block 130. The packet processing block 120 andthe routing control block 130 are application-specific integratedcircuits (ASIC), designed so as to produce the functions of thesecircuits described below.

In the embodiment, the network switching device 1000 includes threeinterface boards 300. Each of the three interface boards 300 has anidentical structure, as so in FIG. 1 the internal structure is shown foronly one of the interface boards 300, and the internal structure isomitted for the other interface boards 300. Each of the interface boards300 includes a TxRx processing block 310 and a plurality of physicalinterface blocks 320. The TxRx processing block 310 is a custom-designedASIC, as is the case for the packet processing block 120 and the routingcontrol block 130. Each physical interface block 320 is connected to anetwork via a line 600, where physical interface conversion, such asoptical/electrical conversion or electrical level conversion isperformed for the packets carried on the lines 600 to convert to datathat can be processed within the interface boards. Coaxial line, opticalfibers, or the like, can be used for the lines 600.

Here the packet processing block 120 of the aforementioned switchingboard 100, and the TxRx processing block 310 of the interface board 300are connected so as to be able to communicate with an external bus 500.Each packet processing block 120 can communicate with each of the TxRxprocessing blocks 310 in the three interface boards 300.

The structure of the network switching device 100 will be explained ingreater detail, referencing FIG. 3, focusing on the switching board 100and the interface board 300. The switching board 100 includes anon-board power supply (OBP) 160 and clock generators CL1 through CL5, inaddition to the packet processing block 120, the routing control block130, and the internal bus 140, described above. Moreover, the interfaceboard 300 includes an on-board power supply (OBP) 360, and clockgenerators CL6 and CL7 in addition to the TxRx processing block 310 andthe physical interface blocks 320, described above.

The on-board power supply 160 supplies electric power to each of theconstituent elements included in the switching board 100, and theon-board power supply 360 supplies electric power to each of theconstituent elements included in the interface board 300, and areconnected to a main power supply 700.

Each of the clock generators CL1 through CL7 includes a high-frequencyoscillator 22, a low-frequency oscillator 23, and a selector 21, asshown for the example of the clock generator CL1 in FIG. 3. Thehigh-frequency oscillator 22 and the low-frequency oscillator 23 use,for example, crystal oscillators, and produce clock signals of specificfrequencies. The frequency of the clock signal produced by thehigh-frequency oscillator 22 is higher than the frequency of the clocksignal produced by the low-frequency oscillator 23. In the below, theclock signal generated by the high-frequency clock oscillator 22 shallbe termed the high-frequency clock signal HH, and the clock signalgenerated by the low-frequency oscillator 23 shall be termed thelow-frequency clock signal HL. The frequency of the high-frequency clocksignal HH is set to, for example, between 1.5 times and 3 times thefrequency of the low-frequency clock signal HL. The selector 21 iscontrolled by the system management block 11 to cause either thehigh-frequency oscillator 22 or the low-frequency oscillator 23 toproduce a clock signal, and then outputs that clock signal. As can beunderstood from the discussion above, each of the clock generators CL1through CL7 can be controlled by the system management block 11 tooutput selectively a clock signal that is either the high-frequencyclock signal HH or the low-frequency clock signal HL.

The clock generator CL1 provides a clock signal to the routing controlblock 130 of the switching board 100, where the routing control block130 operates synchronized with the supplied clock signal. The clockgenerator CL2 and the clock generator CL3 supply clock signals to theinternal bus 140 that connects the routing control block 130 to thepacket processing block 120, and the internal bus 140 operatessynchronized with the supplied clocks. The clock generator CL4 suppliesa clock signal to the packet processing block 120 of the switching board100, where the packet processing block 120 operates synchronized withthe supplied clock. The clock generator CL5 and the clock generator CL6supply clock signals to the external bus 500 that connects the packetprocessing block 120 of the switching board 100 and the TxRx processingblock 310 of the interface board 300, where the external bus 500operates synchronized with the supplied clock. The clock generator CL7supplies a clock signal to the TxRx processing block 310 of theinterface board 300, and the TxRx processing block 310 operatessynchronized with the supplied clock circuit.

The structures of the TxRx processing block 310, the packet processingblock 120, and the routing control block 130 will be explained in moredetail. As is shown in FIG. 3, the TxRx processing block 310 includes aTxRx engine 311 and a memory 312. The packet processing block 120includes a forwarding engine 121 and a memory 122. The routing controlblock 130 includes a forwarding destination search engine 131, a memory132, and a high speed search memory 133. The high speed search memory133 can use, for example, content-addressable memory (CAM). The memory132 stores a forwarding table 134. The high speed search memory 133stores an IP address table 135. The high speed search memory 133 is amemory that is provided with a search function, and can retrieve rapidlythe IP addresses stored in the IP address table 135. Note that theforwarding table 134 and the IP address table 135 are distributed by thesystem management block 11.

A simple explanation of the packet switching process by the networkswitching device 1000 will be given next. The electronic signals for thedata that is transmitted on the lines 600 are converted into bit data bythe physical interface blocks 320 (in a process corresponding to thephysical layer in the OSI (open system interconnection) referencemodel). The TxRx engine 311 of the TxRx processing block 310 recognizesthe data block used in the data link layer in the OSI reference model byinterpreting the bit data. The data block used in the data link layer istermed a “frame,” where there are, for example, Ethernet™ frame. TheTxRx engine 311 of the TxRx processing block 210 extracts, from therecognized frame, the data block that is used in the network layer andsends the extracted data block through the external bus 500 to thepacket processing block 120. The data block used in the network layer istermed a “packet,” such as IP packet. Conversely, the structure may besuch that the TxRx engine 311 sends the frames, without extracting thepackets, with the packets being extracted from the frames in the packetprocessing block 120. The memory 312 is used as a buffer area for thetemporary storage of data such as frames, during processing by the TxRxengine 311. The packet processing block 120, of the plurality of packetprocessing blocks 120 to which the TxRx engine 311 of the TxRxprocessing block 310 will send the packet is either set in advance inthe TxRx processing block 310 by the system management block 11, or isdetermined based on the header data of the frame.

The forwarding engine 121 of the packet processing block 120 storestemporarily, in the memory 122, the packets that have been sent from theTxRx engine 311. The forwarding engine 121 extracts the address datathat is associated with the packets that have been sent (the addressdata corresponds to the “destination-address information” in theclaims). The address data is, for example, header data that includes anIP address. The forwarding engine 121 sends the extracted address datathrough the internal bus 140 to the routing control block 130 within thesame switching board 100.

The routing control block 130 searches the IP address table 135 that isstored in the high speed search memory 133 using the IP address that hasbeen sent as the address data, as the search key. Because pointers areassociated with each IP address stored in the IP address table 135, therouting control block 130 is able to acquire the pointer that isassociated with the IP address that is the search key. The routingcontrol block 130 references the forwarding table 134 stored in thememory 132 to acquire the packet processing data that is associated withthe pointer. The packet processing data describes that data thatspecifies the packet forwarding address, or in other words, data thatspecifies the line that should send the packet. The data that specifiesthe line is, for example, the number of the TxRx processing block 310and the number of the physical interface block 320 to which theapplicable line is connected.

The routing control block 130 sends the acquired packet processing datathrough the internal bus 140 to the packet processing block 120. Theforwarding engine 121 of the packet processing block 120 specifies,based on the acquired packet processing data, one TxRx processing block310 to which the packet should be sent, from among the plurality of TxRxprocessing blocks 310 included in the network switching device 1000. Theforwarding engine 121 sends the packet, along with the correspondingpacket processing data, through the external bus 500 to the specifiedTxRx processing block 310. The TxRx processing block 310, upon receiptof the packet and the packet processing data, sends the packet from thephysical interface block 320 specified based on the packet processingdata. The series of packet switching processes described above areexecuted for each packet that is sent through the line 600 to thenetwork switching device 1000.

FIG. 4 and FIG. 5 will be referenced next to explain the startup processfor the network switching device 1000. FIG. 4 shows an explanatorydiagram of one part of the contents of the settings file. FIG. 5 shows aflow chart of the processing routine in the startup process. The startupprocess is executed when the power supply is turned on or when there isa restart after a problem. When the startup process is initiated, thecontrol board 10 is started up first (Step S110).

When the control board 10 is started up, the system management block 11of the control board 10 reads out the settings file 17 that is stored inthe memory 13 (Step S120). The settings file 17 is a file for storingthe various types of setup information for the user to setup thenetworks switching device 1000. The settings file 17 may, in addition towhat is shown in FIG. 4, include line information such as the types oflines, definitions of link aggregation functions, routing protocolinformation such as definitions pertaining to routing protocol, and soforth. FIG. 4 selectively shows that which is necessary to thedescription of the embodiment, the settings file 17, as shown in FIG. 4,includes running mode specification data that specifies the running modeof the network switching device 1000. The network switching device 1000pertaining to the embodiment can operate in the following five runningmodes:

-   1. Normal power fixed running mode,-   2. Low-power fixed running mode,-   3. Traffic load basis running mode,-   4. Periodic basis running mode, and-   5. Line speed basis running mode.

Moreover, the settings file 17 may include, as settings pertaining tothe traffic load basis running mode, specifications of ranges of trafficand specifications of operation modes corresponding to the ranges oftraffic. The settings file 17 may include, as settings pertaining to theperiodic basis running mode, specifications of time bands andspecification of operation modes corresponding to the time bands.Moreover, the settings file 17 may include, as settings pertaining tothe line speed basis running mode, specifications of line speed rangesand specifications of operation modes corresponding to the line speedranges. These running modes will be described below.

The settings file 17 can include as well non-use record information.Non-use record information include information on “unused interfaces,and data on unused boards. The non-use record information is informationfor recording in advance unused interface boards and unused physicalinterface blocks. The non-use record information is information forspecifying the unused interface boards when there are interface boardsthat are not used (“unused interface boards”) among the plurality ofinterface boards 300, and may use, for example, the identificationnumber of the interface board 300 (which, in the example shown in FIG.4, is “#3”). Moreover, the non-use record information is information forspecifying the unused physical interface blocks when there are physicalinterface block that are not used (“unused physical interface blocks”)among the plurality of physical interface blocks 320, in the respectiveplurality of interface boards 300, and may use, for example, theidentification number of the interface board 300 to which the unusedphysical interface block belongs, in combination with the identificationnumber of the unused physical interface blocks (which, in the exampleshown in FIG. 4, are “#2-2” and “#2-3”).

When the settings file 17 is read out, the system management block 11executes the startup/setup of the each constituent elements in thenetwork switching device 1000 based on the data that is recorded in thesettings file 17 (Step S130). Here the various constituent elements forwhich the startup/setup is executed include not just the systemmanagement block 11, but also all constituent elements such as thepacket processing block 120, the routing control block 130, and theinternal bus 140 of the switching board 100, the TxRx processing block310 of the interface board 300, and the external bus 500.

Explaining in detail, the system management block 11 controls theonboard power supply 160 of the switching board 100 to supply power tothe packet processing block 120, the routing control block 130, and theinternal bus 140. Similarly, the system management block 11 controls theon-board power supply 360 of the interface board 300 to supply power tothe TxRx processing block 310 and the physical interface block 320.Similarly, power is also supplied through the onboard power supply 360to the external bus 500. Note that the system management block 11 turnsoff the output from the onboard power supply 360 of the recordedinterface board 300 when an interface board 300 is recorded as an unusedinterface board in the non-use record information in the settings file17. The result is that the power supply to each of the elements includedin the applicable interface board 300 (including the TxRx processingblock 310, the physical interface block 320, and the clock generatorsCL6 and CL7) included in the applicable interface board 300 will be in astopped state. Similarly, when a unused physical interface block isrecorded in the non-use record information in the settings file 17, thesystem management block 11 either causes the power from the onboardpower supply 360 to not be supplied to the physical interface block 320that is recorded, or make the physical interface block that is recordedin a state in which the power consumption is reduced using an existingtechnology.

Furthermore, when the normal power fixed running mode is setup in thesettings file 17, the system management block 11 controls the variousclock generators CL1 through CL7 to produce and output high-frequencyclock signals HH. This causes the packet processing block 120, routingcontrol block 130, internal bus 140, external bus 500 and TxRxprocessing block 310 to each start up synchronized with thehigh-frequency clock signal HH. Similarly, when any of the three basisrunning modes (traffic basis, periodic basis, or line speed basis) areset in the settings file 17, the packet processing block 120, routingcontrol block 130, internal bus 140, external bus 500, and TxRxprocessing block 310 are each started up with default valuessynchronized with the high-frequency clock signal HH.

On the other hand, if the low-power fixed running mode is set in thesettings file 17, the system management block 11 controls the variousclock generators CL1 through CL7 to produce and output low-frequencyclock signal HL. This causes the packet processing block 120, routingcontrol block 130, internal bus 140, external bus 500, and TxRxprocessing block 310 to startup synchronized with the clock signal HL.After this, in the operation of the network switching device 100, theoperation mode of the respective constituent elements 120, 130, 140,500, and 310 that are synchronized with the high-frequency clock signalHH shall be termed the “high-frequency clock operation,” and theoperation mode of the respective constituent elements 120, 130, 140,500, and 310 that are synchronized with the low-frequency clock signalHL shall be termed the “low-frequency clock operation.” As a generalconcept, speeding up the clock signals, which are a major factor indetermining the operating speed of the various constituent elements, isone means by which to enable high speed packet processing; however,speeding up the clock signals makes the amount of power consumptionincrease due to the increased operating speed of the internalsemiconductor integrated circuits. In the network switching device 1000that uses the various constituent elements using this design method,speeding up the operation clock signals that are supplied to the variousconstituent elements increases the switching capacity by also increasesthe power consumption. Conversely, reducing the speed of the clocksignal can reduce power consumption, but reduces the switching capacity.

When each constituent element of the network switching device 100 isstarted up and setup by the switch control block 11 and networkswitching device 1000 become a state wherein the packet switchingprocess can be operated, then the packet switching process are startedin the network switching device 1000(Step S140), and the startup processis terminated.

Here, as described above, either of the two fixed running modes (thenormal power or low power running mode) or any of the three basisrunning modes (the traffic basis, periodic basis, or line speed basisrunning mode) can be set in the settings file 17. The normal power fixedrunning mode is a running mode where, after running commences, thenetwork switching device 1000 is always running at the high-frequencyclock operation, and the low voltage fixed running mode is a runningmode wherein, after running commences, the network switching device 1000is always running at the low-frequency clock operation. On the otherhand, the basis running modes are running modes wherein, after runningcommences, the operation of the network switching device 1000 switchesautomatically between high-frequency clock operation and low-frequencyclock operation depending on the actual traffic load or the forecastedtraffic load in the packet switching process.

The traffic load basis running mode and the periodic basis running modewill be explained in reference to FIG. 7 through FIG. 8. FIG. 6 shows anexplanatory diagram for explaining the traffic load basis running modeand the periodic basis running mode. FIG. 7 shows a flow chart of theprocessing routine in the frequency control process in the traffic loadbasis running mode. FIG. 8 shows a flow chart of the processing routinein the frequency control process in the periodic basis running mode. InFIG. 6, the horizontal axis shows the time of day, and the vertical axisshows the traffic (the amount of packet flow) per unit time. Theswitching capacity required in the network switching device is notnecessarily always a high value, but rather often may change withrelative regularity depending on the network operating environment. Forexample, in the example illustrated in FIG. 6, there is a suddenincrease in traffic beginning about 7:00 am, with consistently hightraffic from 8:00 am to 6:00 pm. However, the traffic rapidly diminishesbetween 6:00 pm and 8:00 pm, with uniformly low traffic from 8:00 pmthrough 7:00 am the next day, at about ⅓ of the traffic found between8:00 am and 6:00 pm.

When this type of change in traffic level is known to repeat regularly,the user may select, for example, the traffic load basis mode. As shownin FIG. 4, in the traffic load basis settings, if the per-unit-timetraffic load (packets/sec) of the packets is less than M, then thecorresponding operation are set to low-frequency clock operation, and ifthe per-unit-time traffic load is M or more, then the correspondingoperation is set to high-frequency clock operation. The value of M maybe set to an intermediate value between the average traffic load between8:00 am and 6:00 pm and the average traffic load between 8:00 pm and7:00 am the next morning. The frequency control process when the networkswitching device 1000 is in traffic load basis mode will be explainedbelow referencing FIG. 7. When running of the network switching device1000 starts, the traffic check module 15 of the system management block11 detects the current packet traffic load (Step S202). The value usedas the current packet traffic load is, for example, an average packettraffic load over the previous period of time of a specific length (forexample, over the previous five minutes). When the current packettraffic load is detected, the frequency control module 16 of the systemmanagement block 11 references the traffic load basis settings in thesettings file 17 shown in FIG. 4 and selects the operation mode (whichis either low-frequency clock operation or high-frequency clockoperation in the example shown in FIG. 4) corresponding to the currentpacket traffic load that has been detected (Step S204). The frequencycontrol module 16 then determines whether or not the current operationmode of the network switching device 1000 is the same as the operationmode selected in Step S204 (Step S206). If the frequency control module16 determines that the current operation mode is the same as theoperation mode selected in Step 204 (Step S206: Yes), then processingreturns to the process in Step 202, and the process described above isrepeated.

On the other hand, if the frequency control module 16 determines thatthe current operation mode is not the same as the operation modeselected in Step S204 (Step S206: No), then the frequency control module16 changes the operation mode of the network switching device 1000 tothe operation mode selected in Step S204 (Step S208). As a specificexample, with the traffic load basis settings shown in FIG. 4, the casewill be described wherein the current packet traffic load is less than Min step S202, so the low-frequency clock operation is selected as thecorresponding operation mode in Step S204. In this case, if the networkswitching device 1000 is already operating at the low-frequency clockoperation, then the processing returns to Step 202, and if the networkswitching device 1000 is operating at high-frequency clock operation,then the operation mode will be switched over from high-frequency clockoperation to low-frequency clock operation. The changeover of theoperation mode from high-frequency clock operation to low-frequencyclock operation is performed through restarting the various constituentelements 120, 130, 140, 500, and 310 to which the clock signals areprovided by the clock generators CL1 through CL7, described above, andswitching the clock signals generated by these clock generators CL1through CL7 from high-frequency clock signals HH to low-frequency clocksignals HL.

When performing the frequency control process as described above, in atime band wherein the traffic load is high and a large amount ofswitching capacity is required (from 8:00 am to 6:00 pm in the examplein FIG. 6), the network switching device 1000 will operate ahigh-frequency clock operation. On the other hand, in a time bandwherein the traffic load is low and there is not so much of a need forswitching capacity (from 10:00 pm to 7:00 am the next morning in theexample in FIG. 6), the network switching device 1000 will operate withlow-frequency clock operation.

Moreover, with the network environment shown in FIG. 6, the user mayselect the periodic basis running mode. The frequency control processfor running the network switching device 1000 in the periodic basisrunning mode will be described in reference to FIG. 8. When theoperations begin, the frequency control module 16 of the device controlunit 11 determines whether or not the current time has reached Time T1recorded in the settings file 17 (Step S302). If the frequency controlmodule 16 determines that the current time is T1 (Step S302: Yes), thenthe frequency control module 16 references the settings file 17 tochange the operation of the network switching device 1000 to theoperation mode defined in the time range from Time T1 through Time T2(Step S304), and processing return to Step S302. In the example in FIG.4, the operation mode that is specified for the time range from Time T1to Time T2 is low-frequency clock operation, so in Step S304, theoperation of the network switching device 1000 is changed fromhigh-frequency clock operation to low-frequency clock operation.

If the frequency control module 16 determines that the current time isnot T1 (Step S302: No), then the frequency control module 16 determineswhether or not the current time is Time T2 written in the settings file17 (Step S206). If the frequency control module 16 determines that thecurrent time is T2 (Step S306: Yes), then the frequency control module16 references the settings file 17 to change the operation of thenetwork switching device 1000 to the operation mode specified in thetime range from Time T2 through Time T1 (Step S308), and processingreturns to Step S302. In the example illustrated in FIG. 4, theoperation mode specified in the time range from Time T2 through Time T1is high-frequency clock operation, and so in Step S308, the operation ofthe network switching device 1000 is switched over from low-frequencyclock operation to high-frequency clock operation. If the frequencycontrol module determines that the current time is not time T2 (StepS306: No), then processing returns to Step S302.

When the frequency control process is performed as described above,then, as shown in FIG. 6, the network switching device 1000 is operatedat high-frequency clock operation during the time band wherein highswitching capacity is required, and operates with low-frequency clockoperation during the time band wherein such high switching capacity isnot required, in the same way as for the traffic load basis running modedescribed above.

Next FIG. 9 and FIG. 10 will be referenced in describing the line speedbasis running mode. FIG. 9 shows a figure for explaining an autonegotiation function that automatically coordinates the linespeeds/communications modes of a line between a pair ofmutually-connected devices. FIG. 10 shows a flowchart of the processingroutine in the frequency control process in the line speed basis runningmode. The auto negotiation function is a function that coordinatesautomatically the line speeds/communications modes of a line betweenmutually-connected devices. In a communications method established byIEEE (the American Institute of Electrical and Electronics Engineers),there are interfaces having auto negotiation functions. Typicalcommunications methods having auto negotiation include 10 BASE-T/100BASE-X (specified in IEEE 802.3u), 1000 BASE-T (specified in IEEE802.3ab), and 1000 BASE-X (specified in IEEE 802.3z). If the physicalinterface block 320 of the network switching device 1000 supports thesecommunications methods, then, as shown in FIG. 9, when mutuallyconnected with the physical interface block 2020 of an opposite device2000 through a line 600, the physical interface block 320 is able toautomatically adjust the line speeds/communications mode throughchecking the communications capabilities between the physical interfaceblock 320 and the physical interface block 2020 of the opposite device2000, connected through the line 600. Specifically, the mutualcommunications capability is confirmed through the exchange of controlsignals SG for communicating transfer capability data between thedevices. Given this, the line speed/communications mode with the highestpriority, of those modes supported by both devices, is setautomatically. The line speed/communications mode can also be setmanually. When the physical interface block 320 is provided with an autonegotiation function, then the packet traffic coming into the networkswitching device 1000 is determined by the line speed set in each of thephysical interface blocks 320. For example, in a network switchingdevice 1000 wherein ten lines 600 are connected, if the line speed inall of the lines 600 is set to 10 Mbps, then all of the packets can beprocessed if the network switching device 1000 has a switching capacityof 10 Mbps×10 lines=100 Mbps. Moreover, if the line speed for all of thelines 600 is 1000 Mbps, then it would be necessary for the networkswitching device 1000 to have a switching capacity of 1000 Mbps×10lines=10 Gbps.

In this way, the switching capacity required in the network switchingdevice 1000, depending on the results of the line speed negotiations bythe physical interface blocks 320, will not necessarily always be thehigher value. When the user selects the line speed basis running mode,then the user sets the line speed ranges and the corresponding operationmodes in the setting file in consideration of the switching capacitythat can be provided by the operation mode. In the example illustratedin FIG. 4, the operation mode corresponding to the case wherein the sumof the line speeds of all of the lines 600 (hereinafter termed the totalline speed) is less than N is set to the low-frequency clock operation,but the operation mode corresponding to the case wherein the total linespeed is N or greater is set to high-frequency clock operation.

The frequency control process when running the network switching device1000 in the line speed basis running mode will be explained in referenceto FIG. 10. When running of network switching device 1000 starts, theline speed check module 18 of the system management block 11 obtains thecurrent line speeds of each of the lines 600 and determines whether ornot there has been a change in the total line speed (Step 402). Forexample, if a new line 600 has been connected, then there will have beena change in the total line speed. When the line speed check module 18determines that there has been no change in the total line speed (StepS402: No), then monitoring for the occurrence of a change in the totalline speed is continued. If the line speed check module 18 determinesthat a change in the total line speed has occurred (Step S402: Yes),then the sum of the line speed of all of the lines 600 (the total linespeed) is calculated/detected (Step S404). The frequency control module16 of the system management block 11 references the settings file 17 toselect the operation mode corresponding to the total line speed that hasbeen detected (Step S406). The frequency control module 16 determineswhether or not the current operation mode of the network switchingdevice 1000 is the same as the operation mode selected in Step S406(Step S408).

When the frequency control module 16 determines that the currentoperation mode is the same as the operation mode selected in Step S406(Step S408: Yes), then processing returns to Step S402, and theprocesses described above are repeated. On the other hand, when thefrequency control module 16 determines that the current operation modeis not the same as the operation mode selected in Step S406 (Step S408:No), then the operation mode of the network switching device 1000 isswitched over to the operation mode selected in Step S406 (Step S410).As a specific example, an explanation will be given of the case wherein,with the line speed basis setting as shown in FIG. 4, the current totalline speed in Step S404 is less than N, and low-frequency clockoperation has been selected as the corresponding operation mode in StepS406. In this case, if the network switching device 1000 is alreadyoperating in the low-frequency clock operation, then processing returnsto Step S402, but if the network switching device 1000 is operating inhigh-frequency clock operation, then the operation mode is switched fromhigh-frequency clock operation to low-frequency clock operation. Theswitching of the operation mode is performed in the same manner as theswitching of the operation mode for the traffic load basis modedescribed above.

When the frequency control process, described above, is performed, thenetwork switching device 1000 operates with high-frequency clockoperation when the sum of line speeds is high so that the state ofnetwork switching device 1000 is one wherein the high packet trafficload can be anticipated. On the other hand, when the sum of the linespeeds is low, in a state wherein such high switching capacity will notbe required, then the network switching device 1000 operates withlow-frequency clock operation.

As can be understood from the description above, in the embodiment, thefrequency control module 16 switches the operation mode of the networkswitching device 1000 by changing the frequency of the clock signal thatis generated. That is, in this embodiment, the frequency control module16 equivalent to the mode management block in the claims.

The network switching device 1000 in the embodiment, described above,change the frequency of the clock signal supplied to the variousconstituent elements depending on the user settings. This makes itpossible to increase the performance of the network switching device1000 by increasing the processing speed of the semiconductor integratedcircuits (for example, the packet processing blocks 120 and the routingcontrol blocks 130) by increasing the frequency, and makes it possibleto reduce the power consumption of the network switching device 1000 byreducing the processing speed of the semiconductor integrated circuitsby reducing the frequency. The result is that it is possible to controlthe amount of electrical power consumed by the network switching device1000 while maintaining the necessary performance when required.

Moreover, because switching between high-frequency clock operation andlow-frequency clock operation is performed automatically depending onthe traffic load, such as in the periodic basis running mode, thetraffic load basis running mode, and the line speed basis running mode,it is not only possible to maintain a large switching capacity when alarge switching capacity is required, but also possible to reduce theconsumption of electric power when a large switching capacity is notrequired. The result is the ability to control the overall consumptionof electric power without sacrificing switching performance.

Moreover, the user is able to record, in advance, in the settings file17, the interface boards 300 that will not be used. At startup, thesystem management block 11 references the settings file 17 regarding theunused interface boards 300 that have been recorded in the settings file17, to selectively stop the supply of power thereto. The result is thatit is possible to further reduce the amount of electrical powerconsumed.

Moreover, the user is able to record, in advance, in the settings file17, the physical interface blocks 320 that are unused. If there is anunused physical interface block 320 recorded in the settings file 17,then the system management block 11 does not supply electrical powerfrom the on-board power supply 360 to the physical interface block 320that is recorded in the settings file 17, or uses a known technology toset a state of the physical interface block 320 that is recorded in thesettings file 17 wherein power consumption is reduced. The result is aneven greater ability to reduce the consumption of electrical power.

Operation Mode Management Process

FIG. 11 through FIG. 15 are schematic diagrams illustrating in greaterdetail the operation mode management process in this embodiment. Each ofFIG. 11 through FIG. 15 illustrates the operation state of the networkswitching device 1000. In each of these figures, one interface board 300is illustrated as a representative example of all of the plurality ofinterface boards 300.

Note that, as shown in FIG. 1, the network switching device 1000 has twocontrol boards 10 and two switching boards 100. Given this, in theexplanation below, a code identifying the individual is added to theends of the codes indicating the control boards 10 and the switchingboards 100, as well as to the ends of the codes indicating the variousconstituent elements and the various types of data. That is, the code“a” is added to the ends of the codes identifying those items pertainingto the “first” board, and the code “b” is added to the ends of the codesidentifying those items pertaining to the “second” board. Moreover, whenit is not necessary to differentiate between the individual controlboards, or the individual switching boards, or the like, the codes forindividual identification, which are otherwise added to the ends of thecodes, are omitted.

In the first embodiment, one of the two switching boards 100 a and 100 bis used as the “active board” and the other is used as the “standbyboard.” In the example shown in FIG. 11, the first switching board 11 afunctions as the active board and the second switching board 100 bfunctions as the standby board. The same is true for the control boards10. Note that in the explanation below, it is assumed that the firstcontrol board 10 a is always functioning, and the second control board10 b is not used. Note also that in the explanation below, the switchingboard 100 that is functioning as the active board may also be referredto as simply the “active board 100.” The same is true for the “standbyboard.”

Under normal conditions, only the active board 100 a performs the packetswitching process (or, more specifically, performs the process ofdetermining the lines to which to send the packets, also termed“switching-determination process” below), where the standby board 100 bdoes not perform the switching-determination process. The standby board100 b continues the switching-determination process instead of theactive board 100 a when a problem occurs with the active board 100 a. Inthis way, in the first embodiment, there is redundancy in the switchingboards 100, making it possible to increase the reliability when it comesto problems with the switching boards 100. Moreover, as will bedescribed below, the standby board 100 b can also be used in changeoverprocessing of the operation modes in the network switching device 1000.

In order to achieve continuity in the switching-determination processusing the standby board 100 b, the control board 10 (the systemmanagement block 11) reflects to the standby board 100 b any changes inthe forwarding table 134 (FIG. 3) or the IP address table 135 in theactive board 100 a (where these tables 134 and 135 shall be termed,together, the “switching information 134 and 135”). If there is a changein the switching information 134 or 135 in the active board 100 a, thenthe control board 10 changes the switching information 134 or 135 in thestandby board 100 b in the same way as well. This type of change inswitching information can be performed, for example, by userinstructions. Moreover, the control board 10 (system management block11) may update the switching information 134 and 135 automaticallythrough the use of the RIP or OSPF commands.

Changes in the operation statuses when there is a change from the“normal mode” to the “low-power mode” for the operation mode in thenetwork switching device 100 are illustrated in FIG. 11 through FIG. 15.The operation statuses in the network switching device 1000 changesequentially from FIG. 11 through FIG. 15. In the first step S1, shownin FIG. 11, the network switching device 1000 is operating in “normalmode.” In this “normal mode,” the respective switching boards 100 a and100 b, and the respective interface boards 300 are each operating in“normal mode.”

In the present embodiment, the “normal mode” of a switching board 100means that each of the clocks related to that switching board 100 (thatis the core clocks CC for each of the circuits 120 and 130, the busclock RC for the internal bus 140, and the bus clock NC for the externalbus 500 between the packet processing block 120 and the TxRx processingblock 310) are each in the “high” state. Conversely, the “low-powermode” for the switching board 100 means a state wherein each of theseclocks is in the “low” state. Moreover, the “normal mode” for theinterface board 300 means a state wherein the core clock CC of the TxRxprocessing block 310 is “high.” Conversely, the “low-power mode” for aninterface board 300 means a state wherein the core clock CC for the TxRxprocessing block 310 is “low.” Note that although a clock signal fromthe interface board 300 side is also supplied to the external bus 500(FIG. 3: Clock generator CL6), the frequency of this clock signal ischanged depending on the switching over of the operation mode of theswitching board 100 (described below).

In the next step S2 (FIG. 12), the first system management block 11 a(the frequency control module 16 (FIG. 2)) switches the operation modeof the second switching board 100 b from the “normal mode” to the“low-power mode.” The first system management block 11 a eithertemporarily turns the power to the standby board 100 b off and then onagain, or applies a reset thereto, to restart the standby board 100 b.After this, the various clock generators CL1 through CL5 (FIG. 3) of thestandby board 100 b are controlled in the procedure described in StepS130 of FIG. 5 to generate and output the low-frequency clock signal HL.This causes the core clocks CC of the respective circuits 120 b and 130b, the internal bus clock RCb and the external bus clock NCb for thestandby board 100 b to each change from “high” to “low,” causing thestandby board 100 b to perform processing synchronized with thelow-frequency clock signals HL after the change. Note that theswitching-determination process is performed by an active board 100 athat is not the standby board 100 b, so the switching-determinationprocessing continues, without being affected by the restarting of thestandby board 100 b.

Note that “resetting (power-on resetting)” means a process of resettingthe operations of the electronic circuit without turning off the powerto the electronic circuit. Resetting initializes the operation in theelectronic circuit. For example, resetting sets the values that arestored in the memory in the electronic circuit (for example, the ASICregisters) to specific values. Note also that this resetting can beperformed, using a variety of methods. For example, the resetting of theelectronic circuit may be performed by the first system management block11 a applying a specific reset signal to the electronic circuit. Thistype of reset is often used when changing the operation modes ofelectronic circuits. Given this, preferably a reset is performedfollowing setting a new operation mode. Doing so causes theinitialization of the operation of the electronic circuit to beperformed in the operation mode that has been set, thus making itpossible to prevent any instability in the processing of the electroniccircuit that might arise from the change in the operation mode. In thepresent embodiment, the standby board 100 b may be subjected to a resetafter there has been a change in each of the clocks CC, RCb, and NCb.Note that, conversely, the new operation mode may be set after thereset. Note also that the explanation above of changing the operatingmode and performing the reset is the same also for other electroniccircuits (such as the other switching board 100 and the interface boards300).

After the standby board 100 b is restarted, the first system managementblock 11 a copies the switching information 134 and 135 from the activeboard 100 a to the standby board 100 b. This causes the standby board100 b to store the same switching information as the active board 100 a.As a result, the standby board 100 b is capable of executing the sameswitching-determination processes as the active board 100 a. Note thatthe copying of the switching information 134 and 135 is performedthrough the control bus 400 (FIG. 1). Moreover, in this way, the copyingof the switching information is performed after the restarting of thestandby board 100 b has been completed, or in other words, after thechanging of the operation mode of the standby board 100 b has beencompleted. Consequently, even if the memories 132 and 133 (FIG. 3) havebeen cleared as a result of the change in the operation mode, thestandby board 100 b can store the appropriate switching information.

Moreover, the first system management block 11 a controls the clockgenerator CL6 (FIG. 3) of the interface board 300 to cause thegenerating and outputting of the low-frequency clock signal HL. Thiscauses the external bus clock NCb of the external bus 500 in theinterface board 300 to change from “high” to “low” as well. Thischangeover of the external bus clock NCb is performed without restartingthe TxRx processing block 310. For example, the first system managementblock 11 a resets the interface circuitry (for example, a so-calledSERDES (serializer/deserializer) circuitry, not shown) that performcommunications with the standby board 100 b in the TxRx processing block310. In addition, the first system management block 11 a switches theexternal bus clock NCb (the clock from the clock generator CL6 (FIG. 3))during the reset. Note that the packet switching process, or, morespecifically, the packet sending and receiving process (hereinaftertermed the “transfer process”) is performed by an interface circuitry(not shown) for the active board 100 a, which is different from theinterface block that is being reset, and thus the transfer processcontinues, unaffected by the changeover of the external bus clock NCb.

In the next step S3 (FIG. 13), the first system management block 11 aswitches the current active board 100 a with the current standby board100 b. Specifically, the first system management block 11 a sends, tothe TxRx processing block 310, a command to send packets to the secondpacket processing block 120 b instead of to the first packet processingblock 120 a. In response to this command, the TxRx processing block 310begins to send packets to the new active board 100 b. As a result, thepacket switching process by the second switching board 100 b and theinterface board 300 is started. On the other hand, because packets areno longer sent to the first switching board 100 a, the packet switchingprocess (the switching-determination process) is no longer performed bythe first switching board 100 a.

As described above, the second switching board 100 b has the same dataas the switching information in the first switching board 100 a (StepS2: FIG. 12). Consequently, the second switching board 100 b is able tostart a process that is the same as the switching-determination processthat had been being performed by the first switching board 100 a.Moreover, the switching-determination process by the second switchingboard 100 b (the new active board) is started after the conclusion ofthe copying of the switching information, thus making it possible toprevent that interruption of the switching-determination process whichis caused by the swapping (switching over) of these switching boards100.

In the next step S4 (FIG. 14), the first system management block 11 achanges the operation mode of the first switching board 100 a from the“normal mode” to the “low-power mode.” This changeover process isperformed in the same manner as the changeover process for the operatingmode of the second switching board 100 b, explained using FIG. 12. Thereason why, in this way, the operation mode of the new standby board(the switching board 100 that is in the standby state) is changed to thesame mode as the operation mode of the new active board (the switchingboard 100 that is in the operating state) is that if a problem were tooccur in the active board, this makes it possible to use the standbyboard operating in the same operation mode as the active board.

In the next step S5 (FIG. 15), the first system management block 11 achanges the operation mode of the interface board 300 from the “normalmode” to the “low-power mode.” The first system management block 11 arestarts the interface board 300 through either turning off and thenback on the power supply to the interface board 300, or performing areset on the interface board 300. After this, the clock generator CL7(FIG. 3) of the interface board 300 is controlled according to theprocedure explained in Step S130 of FIG. 5 to generate and output thelow-frequency clock signal HL. This causes the core clock CC of the TxRxprocessing block 310 to change over from “high” to “low,” causing theTxRx processing block 310 to perform processing synchronized with thelow-frequency clock signal after the changeover. During this modechanging, the transfer process through the interface board 300 duringthe mode changing is interrupted.

The processes described above causes the operation mode of the networkswitching device 1000 to be switched from the “normal mode” to the“low-power mode.” Conversely, the process of switching over theoperation mode of the network switching device 100 from the “low-powermode” to the “normal mode” is performed through the opposite sequence.

As described above, in the first embodiment, the standby board and theactive board are swapped after completion of the changeover of theoperating mode of the standby board, and thus it is possible tochangeover the operation mode of the switching board 100 that is usedfor executing the switching-determination process without switching overthe operation mode of the switching board 100 that is in execution ofthe switching-determination process. As a result, it is possible tocontrol the consumption of electric power while preventing theinterruption time of the packet switching process from becomingexcessively long. Moreover, in the present embodiment, the switchinginformation is copied from the active board to the standby boardimmediately prior to the swapping of the standby board and the activeboard. Consequently, it is possible for the new active board to executethe same switching-determination processes as the old active boardimmediately when the standby board becomes the new active board.Moreover, because the standby board is used in switching over theoperation mode of the switching board 100, the standby board can stillbe used effectively even when there is no problem with the active board.

Moreover, in the first embodiment, the operation mode of the new standbyboard is changed to be the same mode as the operation mode of the newactive board. Consequently, even if there were a problem with the newactive board, it would be possible to continue theswitching-determination process in the same operation mode by using thenew standby board. As a result, it is possible to prevent aninappropriate drop in packet switching processing capability. This alsomakes it possible to prevent inappropriately high levels of powerconsumption in the network switching device 1000.

Note that the mode management process in the first embodiment can beused also in the event of the operation mode changeover that occurs dueto any of the running modes specified in the settings file 17.

B. Second Embodiment

FIG. 16 through FIG. 20 are schematic diagrams illustrating an overviewof a operation mode management process in a network switching device1001 according to a second embodiment. The structure of this networkswitching device 1001 is the same as the structure of the networkswitching device 1000 according to the first embodiment, describedabove, with the addition of a third switching board 100 c. This thirdswitching board 100 c, as with the other boards 100 a and 100 b, isconnected to a control board 10 and an interface board 300. Moreover,the structure of the third switching board 100 c is the same as theother boards 100 a and 100 b. Note that in FIG. 16 through FIG. 20, onlythe three switching boards 100 a through 100 c, a representativeinterface board 300 and the first control board 10 a are shown as theconstituent elements of the network switching device 1001, and the otherconstituent elements thereof are omitted in the drawings. Moreover, inthe explanation below, the code “c” is added to the ends of the codesfor the elements pertaining to the “third” switching board 100 c.

In the second embodiment, two of the three switching board 100 a through100 c are used as the “active boards,” where the remaining switchingboard is used as a “standby board.” In the example illustrated in FIG.16, the first switching board 100 a and the second switching board 100 bfunction as active boards, and the third switching board 100 c functionsas a standby board. The switching-determination process is distributedbetween these two active boards. For example, the two active boards 100a and 100 b are alternately used by the interface board 300 when aplurality of packets are received by the interface board 300. The reasonfor distributing the switching-determination processes between the twoactive boards is to increase the speed of the switching-determinationprocess, or in other words, to increase the speed of the packetswitching process.

FIG. 16 through FIG. 20 illustrate the changing of the operationstatuses when the operation mode in the network switching device 1001 isswitched over from the “normal mode” to the “low speed mode.” The firstsystem management block 11 a (the frequency control module 16 (FIG. 2)),as with the first embodiment, switches over the operation mode of thenetwork switching device 1001 according to the settings that are storedin a settings file 17 (FIG. 4).

In the first step S11, shown in FIG. 16, the network switching device1001 is operating in the “normal mode”. In the “normal mode,” each ofthe switching boards 100 a through 100 c and the interface board 300 isoperating in the “normal mode.”

In the next step S12 (FIG. 17), the operation mode of the standby board100 c is switched from the “normal mode” to the “low-power mode.” Atthis time, the switching information 134 and 135 of one of the activeboards (the active board 100 a) is copied to the standby board 100 c.Furthermore, the external bus clock NCc for the standby board 100 c inthe interface board 300 is also switched over from “high” to “low.”These processes are performed in the same manner as the processes inFIG. 12.

In the next step S13 (FIG. 18), the standby board 100 c is swapped withthe one of the active boards (the active board 100 a). This process isperformed in the same manner as the process in FIG. 13. Note that any ofthe current active boards can be used to be swapped. For example, aboard that has been selected in advance may be used.

In the next step S14 (FIG. 19), the operation mode of the new standbyboard 100 a is switched from the “normal mode” to the “low-power mode.”At this time, the switching information 134 and 135 of the remainingactive board 100 b, which is processing in the normal mode, is copied tothe new standby board 100 a. Furthermore, the external bus clock NCa forthe new standby board 100 a in the interface board 300 is also switchedover from “high” to “low.” These processes are performed in the same wayas the processes in FIG. 12.

In the below, the operating mode of the remaining active board 100 b isalso similarly switched over from the “normal mode” to the “low-powermode” by swapping this active board 100 b with the new standby board 100a. In this way, it is possible to switch the operation modes of all theswitching boards 100 a through 100 c from the “normal mode” to the“low-power mode.” Note that all of the changeovers are performed usingstandby boards, so the packet switching process continues withoutinterruption.

In the next step S15 (FIG. 20), the operating mode of the interfaceboard 300 is switched from the “normal mode” to the “low-power mode.”This process is performed in the same manner as the process in FIG. 15.

The operation mode of the network switching device 1001 is switched overfrom the “normal mode” to the “low-power mode” through the processesdescribed above. Conversely, the process for switching the operationmode of the network switching device 1001 from the “low-power mode” tothe “normal mode” is performed in the opposite sequence of that which isdescribed above.

As described above, in the second embodiment, the series of processesfor swapping the standby board and the active board after the changeoverof the operation mode of the standby board has been completed isperformed repetitively. Consequently, even when the operation mode isswitched over in three of the switching boards 100 a through 100 c, itis still possible to prevent the interruption time of the packetswitching process caused by the switching over of the operation modefrom becoming excessively long.

Note that the total number of the active boards is not limited to one ortwo, but rather any number of active boards, even three or more, may beemployed. Moreover, the number of standby boards is not limited to one,but rather any number of standby boards, even two or more, may beemployed. In any case, at least one of the plurality of switching boards100 may be used as a standby switching block (a standby board 100 in thepresent embodiment) that is started in the same operation mode as anactive board 100 without performing the switching-determination processunless there is a problem. Doing this makes it possible to continue theswitching-determination process using the standby switching block, usingthe same operation mode, when a problem occurs in an active board 100.Furthermore, when the operation mode of a switching board 100 that isused for executing the switching-determination process is switched over,preferably that series of processes described above is performedrepetitively, in which the standby switching block (the standby board100) and an active board 100 are swapped. Doing so makes it possible tochange over the operation mode of the switching board 100 that is usedfor executing the switching-determination process, without switchingover the operation mode of a switching board 100 that is in execution ofthe switching-determination process. As a result, it is possible tochange over the operation mode of a plurality of switching boards 100while preventing the interruption time of the packet switching processfrom becoming excessively long.

Note that the mode management process in the second embodiment can beused also in the event of the operation mode changeover that occurs dueto any of the running modes specified in the settings file 17.

C. Third Embodiment

FIG. 21 through FIG. 25 are schematic diagrams illustrating an overviewof the operation mode management process in a network switching device1002 according to a third embodiment. The difference with the networkswitching device 1001 according to the second embodiment, shown in FIG.16 to FIG. 20 is the point that one of the three switching boards 100 athrough 100 c is used as a “spare board.” In this embodiment, the totalnumber of the active board is one, and the total number of the standbyboard is one. In the example illustrated in FIG. 21, the first switchingboard 100 a functions as the active board, the second switching board100 b functions as the standby board, and the third switching board 100c is used as the spare board. The “spare board” preferably has the powersupply thereto turned off under normal conditions. Moreover, theoperation mode of the spare board may be set to a operation mode withless power consumption than that of the “standby board.” The “spareboard” is provided with power and used as a new standby board when aproblem has occurred in at least one of the “active board” or the“standby board.” Moreover, in the present embodiment, as will bedescribed below, the spare board is used also in the changeover processfor the operation mode of the network switching device 1002. Note thatthe structure of the network switching device 1002 is the same as thestructure of the network switching device 1001 according to the secondembodiment described above.

FIG. 21 through FIG. 25 illustrate the changes in the operation statuseswhen the operation mode of the network switching device 1002 is switchedover from the “normal mode” to the “low-power mode.” The operationstatuses of the network switching device 1002 change in the sequence ofFIG. 21 through FIG. 25. The first system management block 11 a (thefrequency control module 16 (FIG. 2)) switches over the operation modeof the network switching device 1002 according to the settings that arestored in the settings file 17 (FIG. 4) in the same manner as in thefirst embodiment.

In the first step S21 shown in FIG. 21, the network switching device1002 performs processing in the “normal mode.” In this “normal mode,”each of the active board 100 a, the standby board 100 b, and theinterface board 300 is operating in the “normal mode.” Moreover, in thepresent embodiment, the power to the spare board 100 c is turned offunder normal circumstances. Given this, in Step S21, the first systemmanagement block 11 a turns on the power supply to the spare board 100 cin order to perform the operation mode management process. At this time,the operation mode of the spare board 1000 c is set to the “low-powermode.” Moreover, the first system management block 11 a copies theswitching information 134 and 135 of the active board 100 a to the spareboard 100 c. Moreover, if the external bus clock NCc for the spare board100 c in the interface board 300 is “high,” then the first systemmanagement block 11 a switches this external bus clock NCc over to“low.” These processes are executed in the same way as the processes inFIG. 12. Moreover, these processes cause the spare board 100 c tofunction as the new standby board. As a result, the status of thenetwork switching device 1002 becomes a status wherein one active board100 a and two standby board 100 b and 100 c are operating. Note that,the operation mode of the new standby board 100 c is the “low-powermode,” which is different from the operation modes of the other boards100 a and 100 b (which are operating in the normal mode).

In the next step S22, (FIG. 22), the new standby board 100 c and theactive board 100 a are swapped. This process is performed in the sameway as the process in FIG. 13.

In the next step S23 (FIG. 23), the operating mode of the old standbyboard 100 b is switched over from the “normal mode” to the “low-powermode.” Moreover, the external bus clock NCb for the old standby board100 b in the interface board 300 is also switched over from “high” to“low.” These processes are performed in the same way as the process inFIG. 12. Note that in this step S23, the switching-determination processcan be performed by the new standby board 100 a instead of the newactive board 100 c, even in the middle of the process of switching overthe operation mode of the old standby board 100 b.

In the next step, S24 (FIG. 24), the first system management block 11 auses the new standby board 100 a as a new spare board. Specifically, thefirst system management block 11 a switches off the power to the newspare board 100 a. At this time, the external bus clock NCa for the newspare board 100 a may be maintained unchanged at “high,” or, instead maybe switched over from “high” to “low.” If the external bus clock NCa ismaintained at “high,” then when next the operation mode of the networkswitching device 1002 is switched over to the normal mode, there will beno need to change over the external bus clock NCa, making it possible tochange over to the normal mode rapidly. Moreover, if the external busclock NCa is switched over to “low,” then it will be possible tosuppress the power consumption in the interface board 300. Moreover,conversely the provision of the external bus clock NCa to the interfacecircuitry (not shown) within the TxRx processing block 310 may be turnedoff for the new spare board 100 a.

In the next step 25 (FIG. 25), the operation mode of the interface board300 is switched over from the “normal mode” to the “low-power mode.”This process is performed in the same way as the process in FIG. 15.

The operation mode of the network switching device 1002 is switched overfrom the “normal mode” to the “low-power mode” through the processdescribed above. Conversely, the process for switching over theoperation mode of the network switching device 1002 from the “low-powermode” to the “normal mode” is performed following the oppositeprocedure.

As described above, in the third embodiment, the series of processes forswapping the spare board and another switching board 100 (including theactive board and the standby board) after the setting of the operationmode of the spare board has been completed. Consequently, even when theoperation modes of each of the switching boards 100 a through 100 c areto be switched over, it is still possible to prevent any excessivelylong interruptions in the packet switching process caused by switchingover the operation modes.

Moreover, in the third embodiment, a spare board is used in addition tothe active board and the standby board in order to change over theoperating mode of the network switching device 1002, making it possibleto insure the active board and the standby board even when the spareboard is being restarted. Consequently, even when a problem occurs inthe active switching board 100 while the operation mode management(changing) is in process, it is still possible to prevent a long stop inthe packet switching process, by using the standby board 100.

Note that even though in the third embodiment the power supply to thespare board 100 was turned off during normal operations, conversely, thepower supply to the spare board 100 may be turned on during normaloperations. More specifically, two of the three boards, of the switchingboards 100 a, 100 b and 100 c may be used as standby boards. Doing somakes it possible to further increase the reliability to problems of theswitching boards 100.

Typically, at least two of the plurality of switching boards 100 arepreferably used as switching boards 100 for replacements that are notused in the switching-determination process under normal circumstances.Moreover, at least one replacement switching board is preferably startedup in the same operation mode as the active switching boards 100 whichare in operation (that replacement switching board corresponds to the“standby switching block” in the claims). Here, as in the thirdembodiment, that series of processes may be executed repetitively bywhich the operation modes of the replacement switching boards 100 (thespare board in the example in FIG. 21 through FIG. 25) other than thestandby switching block is switched over (set), and after the changeover(setting), the replacement switching board 100 for which the changeoverhas been completed is swapped with another switching board 100. Doing somakes it possible for the standby switching block to perform theswitching-determination process instead of the active board 100 even inthe middle of switching over of the operation mode. As a result, it ispossible to increase the reliability in terms of a problem in theswitching board 100. Here the operation mode of the replacementswitching boards 100 aside from the standby switching block ispreferably set to an operating mode with less power consumption thanthat of the standby switching block. Doing so makes it possible toreduce the power consumption of the network switching device. Note that,any given operation mode may be employed in which the power consumptionis less than that of the standby switching block, as the operation modeof the replacement switching boards 100 aside from the standby switchingblock. For example, a “stop mode” wherein the power supply is turned offmay be employed.

Note that in the third embodiment, a sequence of processes was usedwherein after the spare board 100 c was set to the “low-power mode,” thenew standby board 100 c was swapped with the active board 100 a, the oldstandby board 100 b was switched over to the “low-power mode,” and thenew standby board 100 a was used as the new spare board and the powersupply thereto was turned off; however this sequence may also be changedinstead.

For example, a sequence may be used wherein, after the spare board 100 chas been set to the “low-power mode,” the new standby board 100 c andthe active board 100 a are swapped, the new standby board 100 a is setto the “low-power mode,” and the power supply to the old standby board100 b is turned off as being the new spare board. Note that in thiscase, it is possible for the old standby board 100 b to perform theswitching-determination process instead of the new active board 100 ceven in the middle of switching over the operation mode of the newstandby board 100 a.

Moreover, a sequence such as described below may be used. For example,the old standby board 100 b is set to the “low-power mode” after thespare board 100 c has been set to the “low-power mode” as the newstandby board. In this case, it is possible for the new standby board100 c to perform the switching-determination process instead of theactive board 100 a, even in the middle of the process of switching overthe operation mode of the old standby board 100 b. After this, one ofthe standby board 100 b and the standby board 100 c is swapped with theactive board 100 a, and the new standby board 100 a is used as the newspare board, and the power supply to the new spare board is turned off.

Note that the mode management process in the third embodiment can beapplied in the event of the operation mode changeover that occurs due toany of the running modes specified in the settings file 17.

D. Variations

Note that, in the constituent elements in each of the embodimentsdescribed above, elements aside from the elements claimed in independentclaims are additional elements, and may be omitted as appropriate. Theinvention is not limited to the embodiments set forth herein, and may bereduced to practice in various other ways without departing from thespirit thereof, such as the following variants.

The hardware structure of the network switching device 1000 in theembodiment is merely one example, and the present invention is notlimited thereto. The following illustrates examples of other hardwarestructures as a first variation and as a second variation.

First Variation:

FIG. 26 shows a block diagram of the structure of a network switchingdevice 1000 a pertaining to a first variation. While in the networkswitching device 1000 in the embodiment described above the controlboard 10 and the switching board 100 are separate, in the networkswitching device 1000 a pertaining to the first variation, there is nocontrol board 10, but rather a system management block 11 is provided ina switching board 100. The functions of the other structures andcomponents are the same as in the embodiment, and so the same codes asin FIG. 1 are used in FIG. 26 as well, and explanations thereof areomitted. Even in the network switching device 1000 a pertaining to thefirst variation, it is possible to obtain the same operation and effectsas in the embodiment. Moreover, although a figure is omitted, one boardmay includes the constituent elements of the switching board 100 in FIG.26 and the constituent elements of the interface board 300 in FIG. 26.

Second Variation:

FIG. 27 shows a block diagram of the structure of a network switchingdevice 1000 b pertaining to a second variation. While in the networkswitching device pertaining to the embodiment described above, therewere two switching boards 100, in the network switching device 1000 bpertaining to the second variation, three switching boards 100 areprovided. Of the three switching boards 100, two are active boards thatperform the packet switching process under normal conditions, and theremaining switching board 100 is a standby board that performs theswitch packet processing instead of the active board when failures occurin one of the active boards. In other words, one switching board 100 isa redundant switching board 100.

Here, under normal conditions, that is, during the period of timewherein the standby board is not used for the packets switching process,the system management block 11 prevents a supply of the clock signal tothe various structure elements (the packet processing block 120, therouting control block 130, the internal bus 140, and so forth) of thestandby board 100. Doing so, overall consumption of electric power bythe network switching device 1000 is reduced. Note that when there is afailure in one active board, the provision of the clock signal to eachof the constituent elements in the standby board is restarted, where thesettings of the another active board wherein no problem has occurred,for example, the content of the forwarding table 134, the content of theIP address table 135 are copied to the standby board through the controlbus 400. This makes it possible to swap the standby board 100 with theone active board quickly when a problem occurs. Note that preferably inthe standby board, only the control circuit of the control bus 400 forthe control board 10 to communicate with the standby board 100 should besupplied with the clock signal and be in a state capable of performingcommunications, in order to perform the swapping without problems.Moreover, when it comes to communications through the control bus 400,preferably the process of confirming that communications are performednormally is performed at regular periods during normal operations.

The network switching device 1000 in the embodiment described aboveincludes two switching boards; however, the network switching device1000 b in the second variation includes three switching boards 100, asshown in FIG. 27. It is possible to increase the switching capacity byhaving two of the three switching boards 100 operate in parallel asactive boards to perform the packet switching processes. One of theswitching boards 100 is used as standby board if a failure occurs ineither of the two switching boards 100 as active boards.

If there is no need for a large switching capacity in the networkswitching device 1000 b in the second variation (for example, between8:00 pm and 7:00 am the next morning in FIG. 6), then the device controlunit 11 makes the active board into only a single switching board 100,and makes the other two switching boards 100 into standby boards. Inthis case, the provision of the clock signal to the various constituentelements in the standby boards may be halted. Doing so reduces theoverall switching capacity of the network switching device 1000 bbecause the single active board performs the packet switching processes,but this makes it possible to reduce the consumption of electricalpower. The switching of active and standby may be performed dynamicallybased on monitoring of the traffic load in the network switching device1000 b as a whole. For example, if the traffic load is above a specificthreshold, then two switching boards 100 are caused to perform processesas the active board, but when the traffic load is less than a specificthreshold value, then a single switching board 100 is caused to performprocesses as the active board. Doing this makes it possible to bothmaintain a large switching capacity when the switching capacity isrequired, and to reduce the electrical power consumption when theswitching capacity is not required.

The switching board 100 in the embodiment described above are providedwith a single set of a packet processing block 120, a routing controlblock 130, and an internal bus 140 (hereinafter termed the “switchingprocessing set”), but in the second variation the switching board 100 isprovided with two switching processing sets, as shown in FIG. 27. Theswitching capacity can be increased by performing the packet switchingusing the two switching processing sets in parallel.

In the network switching device 1000 b pertaining to the secondvariation, the system management block 11 may stop the provision of theclock signal to a single switching processing set when there is no needfor a particularly large switching capacity (for example, between 8:00pm and 7:00 am the next morning in FIG. 6). Doing so causes theremaining one switching processing set to perform the packet switchingprocess by itself, reducing the switching capacity of the device as awhole, but making it possible to reduce the electric power consumption.Switching between stopping and supplying the clock signal in this waymay be performed dynamically based on monitoring of the traffic load inthe network switching device 1000 as a whole. For example, if thetraffic load is above a specific threshold, then two switchingprocessing sets are caused to perform the packet switching, but when thetraffic load is less than a specific threshold value, then a singleswitching processing set is caused to perform the packet switching.Doing this makes it possible to both maintain a large switching capacitywhen the switching capacity is required, and to reduce the electricalpower consumption when the switching capacity is not required.

Third Variation:

Although in the embodiment described above clock signals of twodifferent frequencies were generated through the provision of twofrequency oscillators 22 and 23 in the clock generators CL1 through CL7,the type of generating the clock signals is not limited there to. Forexample, the clock generators may be provided with a single frequencyoscillator and a frequency multiplier circuit that multiplies the clocksignal by a specific multiplication ratio. Note that the frequencymultiplier circuit may be provided within the elements to which theclock signals are applied (such as the packet processing block 120).Note that the control of the frequency multiplier circuit by the systemmanagement block 11 may be performed through the transmission of a highor low control signal to the frequency multiplier circuit via a signalline, and may be performed through writing a flag to a control registerfor the frequency multiplier circuit.

Fourth Variation:

Although in the embodiment described above, the operation modes in thenetwork switching device 1000 were controlled at the two levels ofhigh-frequency clock operation versus low-frequency clock operation,control may be performed instead with multilevel operation modes.Specifically, the structure may be one wherein all or part of the clockgenerators CL1 through CL7 may be structured so as to be able togenerate three or more different frequencies, where the frequencies ofthe clock signals that cause the network switching device 1000 tooperate may be changed to multiple levels depending on the traffic ordepending on a user setting. Conversely, multilevel operation modes maybe performed through changing a portion of the clock generators CL1through CL7 stepwise, rather than changing the clock generators CL1through CL7 simultaneously. Specifically, the state wherein all of theclock generators CL1 through CL7 generate the high-frequency clocksignal HH can be defined as a first operation mode. The state whereinthe clock generators CL1 through CL4, which provide the clock signals tothe packet processing block 120, the routing control block 130, and theinternal bus 140, are caused to generate the low-frequency clock signalHL, and clock generators CL5 through CL7, which provide clock signals tothe external bus 500 and the TxRx processing block 310 are caused togenerate the high-frequency clock signal HH may be defined as a secondoperation mode. The state wherein all of the clock generators CL1through CL7 are caused to generate the low-frequency clock signal HL maybe defined as a third operation mode. Moreover, the network switchingdevice 1000 may be operated through selecting any of the first throughthird operation modes depending on the traffic load or on a usersetting. Here it is possible to change flexibly the balance between theprocessing performance and the power consumption in the networkswitching device 1000 through being able to change independently theclock signals that are provided to the switching board 100, theinterface board 300, and the external bus 500.

Fifth Variation:

The clock frequency may be changed without restarting (resetting thepower supply) for some kinds of circuitry among the electronic circuitrythat operate synchronized with the clock signals. In the variousexamples of embodiment described above, the switching board 100 and theinterface board 300 (FIG. 3) may be structured using such kind ofelectronic circuitry. Such a case makes it possible to omit theprocesses to reset the power supplies (turn off and on the powersupplies) of the boards 100 and 300 in the processes that change overthe clock frequencies that are used by these boards 100 and 300 (forexample, Step S2 in FIG. 12 and Step S5 in FIG. 15). However, even insuch a case, when the clock frequency is switched over during theexecution of packet switching processing, a problem could occur in thepacket switching process. Consequently, when the clock frequency of theswitching board 100 used in the switching-determination process ischanged, it is still preferable to swap the switching board 100 forwhich the clock frequency has been changed with another switching board100 (for example, the active board 100), after the clock frequencychanging has been completed for the switching board 100 that is not inexecution of the packet switching process (that is, a standby board or aspare board), in the same manner as in the various embodiments describedabove. Furthermore, even when using an electronic circuitry that doesnot require a power supply reset, preferably a reset (a power-on reset)is still performed after changing the clock frequency. Doing so makes itpossible to prevent the occurrence of problems in the operation of theelectronic circuitry caused by changing the clock frequency. Note that,this reset (power-on reset) may be omitted.

Sixth Variation:

In the embodiments described above, a switching board 100 whose powersupply is turned off under normal circumstances may be used to changeover the operation mode of a switching board 100 that is used in theswitching-determination process. For example, in the embodimentsillustrated in FIG. 11 through FIG. 15, the power supply for the standbyboard 100 may be turned off under normal circumstances. Specifically, inStep S1 (FIG. 11), the power supply to the second switching board 100 bmay be turned off. In the next step, Step S2 (FIG. 12), the systemmanagement block 11 may startup the second switching board 100 b in the“low-power mode” instead of switching over the operation mode in thisboard 100 b. Moreover, after this startup process has been completed,the system management block 11 may swap the first processing board 100 awith the second processing board 100 b (Step S3 (FIG. 13)). Moreover, inStep S4 (FIG. 14), the system management block 11 may turn off the powersupply to the first switching board 100 a instead of switching over theoperation mode of this board 100 a. Conversely, when the operation modeof a switching board 100 is switched over to the “normal mode,” thesystem management block 11 may start up a switching board 100 that isstanding by (with the power supply turned off) with the “normal mode”settings. The processing thereafter may be executed following thereverse sequence. These are true also for the second embodimentillustrated in FIG. 16 through FIG. 20.

Moreover, the same is true in the third embodiment illustrated in FIG.21 through FIG. 25. Specifically, in Step S21 (FIG. 21) the power supplymay be turned off for the spare board 100 c. In the next step, Step S22(FIG. 22), the system management block 11 may startup the thirdswitching board 100 c with the “low-power mode” settings instead ofswitching over the operation mode of this board 100 c. After this, whenthe startup process has been completed, the system management block 11may copy the switching information from the first switching board 100 ato the third switching board 100 c. The next steps S23 (FIG. 23) andStep S24 (FIG. 24) may be the same as in the third embodiment. In StepS23, the system management block 11 may swap the first switching board100 a and the third switching board 100 c. Moreover, in the next stepS24, the system management block 11 may change over the operation modeof the first switching board 100 a to the “low-power mode.” Once thisswitching has been completed, the system management block 11 may turnoff the power supply to the second switching board 100 b, instead ofswitching over the operation mode of this board 100 b, and may use thefirst switching board 100 a as the new standby board. Conversely, whenthe operation mode of a switching board 100 is to be switched over tothe “normal mode,” the system management block 11 may start up theswitching board 100 that is standing by (with the power supply off) with“normal mode” settings. The processes thereafter may be performedfollowing the opposite sequence.

Seventh Variation:

In the various embodiment described above, the core clock CC of the TxRxprocessing block 310 may maintain a constant value regardless of theoperation mode of the network switching device (such as the networkswitching device 1000 in FIG. 1). This makes it possible to change theoperation mode of the network switching device without interrupting thepacket switching process because it is not necessary to restart the TxRxprocessing block 310 when switching over the operation mode of thenetwork switching device. For example, the core clock CC of the TxRxprocessing block 310 may be “high” regardless of the operation mode ofthe network switching device 1000. In this case, the Step S5 (FIG. 15),the Step S15 (FIG. 20), and the Step S25 (FIG. 25) may be omitted.Regardless of the operation mode of the network switching device, theinterface board 300 operates in the “normal mode.”

Note that when the operation mode of the network switching device is inthe “normal mode,” the operation mode of the interface board 300 may bethe “normal mode,” and, conversely, when the operation mode of thenetwork switching device is in the “low-power mode” the operation modeof the interface board 300 may be the “low-power mode”, as in thevarious embodiments described above. This makes it possible to furtherreduce the power consumption of the network switching device in the“low-power mode” of the network switching device. Note that the timingwith which the operation mode of the interface board 300 is changed(Step S5 in FIG. 15, Step S15 in FIG. 20, and Step S25 in FIG. 25) isnot limited to being after completion of the change in the operationmode in the switching board 100, but any given timing may be applied.For example, the timing may be prior to the start of the changing of theoperation mode in the switching board 100, or may be during the changingof the operation mode in the switching board 100.

Note that the system management block 100 preferably has both a firstchangeover mode including changing over the operation mode in theinterface board 300, and a second changeover mode without changing overthe operation mode in the interface board 300, as changeover modes forthe operation modes of the network switching device. Doing so makes itpossible for the network switching device to respond to both the needsof the user who emphasizes the continuity of the packet switchingprocess, and of the user who emphasizes reducing power consumption. Notethat the first changeover mode is a mode wherein the operation mode ofthe interface board 300 is changed over when the operation mode of thenetwork switching device is changed over, the same as in the embodimentsdescribed above. Furthermore, the second changeover mode is a modewherein the operation mode of the interface board 300 is not changedwhen the operation mode of the network switching device is changed over.Not that, the operation mode of the interface board 300 corresponds tothe “forwarding-operation mode” in the claims.

Here, the system management block 11 preferably allows the user toselect the changeover mode to be used in the operation mode change overprocess (operation mode management process). Doing so makes it possibleto cause the changeover mode to conform to the user preferences.Specifically, the system management block 11 may receive a userinstruction, and may selectively perform the mode management processaccording to the first changeover mode if the user instruction hasspecified the first changeover mode, and may selectively perform themode management process according to the second changeover mode if theuser instruction has specified the second changeover mode. The systemmanagement block 11 may receive a user instruction from any given inputdevice that is connected to the system management block 11 (such as anoperating panel, a mouse, or a keyboard). Moreover, the content of theuser instruction that has been received may be recorded in the settingsfile 17 (FIG. 4).

Note that, the conditions for selecting the changeover mode are notlimited to the condition following the user instruction such asdescribed above, but any given condition may be employed. For example,the second changeover mode, which has the shorter interruption time, maybe selected when the number of lines connected to the network switchingdevice is greater than a specific threshold value. Furthermore, thefirst changeover mode, which is able to better suppress the powerconsumption, may be selected when that number of lines is less than thatthreshold value. Here the system management block 11 may select thechangeover mode automatically based on a comparison of the number oflines (for example, the number of physical interface blocks inoperation) to the threshold value.

Eighth Variation

In each of the embodiments described above, any given form may be usedas the form of the “normal mode” and the “low-power mode” of each of theelements in the network switching device (for example, for the switchingboard 100 and the interface board 300 in FIG. 3) insofar as the powerconsumption in the “low-power mode” is less than the power consumptionin the “normal mode.” For example, the frequency of part of the variousclock signals pertaining to the switching board 100 (FIG. 11) (forexample, the internal bus clock RC) may be maintained at a specificvalue regardless of the operating mode of the switching board 100.Moreover, the switching board 100 may have a plurality of electroniccircuits that can operate independently from each other, and all of thecircuits may operate in the normal mode, on the other hand, the powersupply to part of the circuits may be turned off in the low-power mode.

Note that it is preferable to employ a form in which each of theswitching block (for example, the switching board 100 in FIG. 3) and theinterface block (for example, the interface board 300 in FIG. 3)includes electronic circuitry that operate synchronized with clocksignal, and the operation modes is switched by switching the clockfrequencies. Doing so makes it possible to change the power consumptioneasily while preventing complexity in the structure of the electroniccircuitry. In any case, the total number of operation modes that can beused is not limited to 2, but rather any given number of operationmodes, even three or more, may be employed. Moreover, in any case, it ispreferable to reset (power-on reset) the switching block after theoperation mode of the switching block has been set. Doing so makes itpossible to prevent the occurrence of problems in the operation in theswitching block caused by the operation mode being set.

Ninth Variation:

In each of the embodiments described above, the switching informationneed not be limited to information that is the combination of theforwarding table 134 and the IP address table 135, but rather any giveninformation may be employed that establishes the correspondencerelationship between the destination address information of packet andthe line to which the packet should be sent. For example, theinformation may be employed which establish the correspondencerelationship between the MAC address in an Ethernet™ and the line towhich the packet should be sent.

Moreover, in some cases a plurality of physical lines may be combinedtogether and used as a single virtual line (for example, when using alink aggregation function). In such a case, preferably the switchinginformation is set so that all of the plurality of lines in one virtualline is selected as the line to which the packet should be outputted.

Other Variations:

A portion of the structure that is achieved in hardware in theembodiment described above may be achieved in software instead, or,conversely, a portion of the structure that is achieved in software inthe embodiment described above may be achieved in hardware instead. Forexample, in the examples of embodiment described above, the packetprocessing block 120 and the routing control block 130 are structuredfrom an ASIC, but instead may be structured from a general-use processorand a program.

While the present invention have been shown and described on the basisof the embodiments and variations, the embodiments of the inventiondescribed herein are merely intended to facilitate understanding of theinvention, and implies no limitation thereof. Various modifications andimprovements of the invention are possible without departing from thespirit and scope thereof as recited in the appended claims, and thesewill naturally be included as equivalents in the invention.

Various aspects of the invention are previously discussed in thisspecification. In an aspect, the one or more second switching blockspreferably include at least one standby switching block. The standbyswitching block has been started up in a same determination-operationmode as the first switching block and is not performing theswitching-determination process. Furthermore, the standby switchingblock is configured to perform the switching-determination process inplace of the first switching block when a problem occurs with the firstswitching block.

In this arrangement, it is possible to continue theswitching-determination process using the same operation mode, using thestandby switching block, when a problem occurs with the first switchingblock.

In the above network switching device, the system control blockpreferably uses the standby switching block as the target switchingblock.

In this arrangement, it is possible to use efficiently the standbyswitching block even when there is no problem with the first switchingblock.

In the above network switching device, the second switching blocks,preferably, further include at least one spare switching block whosedetermination-operation mode is set to a determination-operation modewith even less power consumption than the standby switching block, andthe system control block uses the spare switching block as the targetswitching block.

In this arrangement, it is possible to increase the reliabilityregarding the problems with the switching blocks, even when changing thedetermination-operation modes, because even if the operation mode of thespare switching block as the target switching block is in the process ofbeing set, the standby switching block is in a backup state that is ableto perform the switching-determination process instead of the firstswitching block.

In the above network switching device, the system control blockpreferably resets the target switching block following setting thedetermination-operation mode of the target switching block.

Resetting the target switching block in this way makes it possible toprevent the occurrence of problems in the operation of the targetswitching block due to the setting of the operation mode.

In each of the above network switching devices, the system control blockpreferably performs (C) a process of switching thedetermination-operation mode of the first switching block to the samedetermination-operation mode as the target switching block aftercompletion of the switchover process.

In this arrangement, it is possible to continue theswitching-determination processes using the same determination-operationmode by the first switching block when a problem has occurred in thetarget switching block that is in execution of theswitching-determination processes.

In each of the above network switching devices, the interface block,preferably, is provided with a plurality of switchableforwarding-operation modes as operation modes of sending and receivingthe packets. The plurality of forwarding-operation modes includes afirst forwarding-operation mode and a second forwarding-operation modewith less power consumption than the first forwarding-operation mode.Furthermore, the mode-process is provided with: a first changeover modeincluding changing over the forwarding-operation modes; and a secondchangeover mode without changing over the forwarding-operation modes. Inthe mode-process in the first changeover mode, the system control blockperforms: (A1-1) setting the interface block into the firstforwarding-operation mode when the determination-operation mode of thetarget switching block is set to the first determination-operation mode;and (A1-2) setting the interface block into the secondforwarding-operation mode when the determination-operation mode of thetarget switching block is set to the second determination-operationmode.

In this arrangement, it is possible to use a first changeover modeincluding changing over the forwarding-operation modes, and a secondchangeover mode without changing over the forwarding-operation modes,thus it is possible to operate with the priority on reducing powerconsumption, and to operate with the priority on the continuity of thepacket switching process.

In each of the above network switching devices, preferably, the firstswitching block comprises a first memory and the second switching blockcomprises a second memory. The first memory and the second memory storeswitching-information. The switching-information is used in theswitching-determination process, and the switching-informationassociates the destination-address information with the line.Furthermore, the system control block performs (D) copying theswitching-information stored in the first memory of the first switchingblock to the second memory of the target switching block, prior tostarting the switching-determination process using the target switchingblock, after completion of the process of setting thedetermination-operation mode of the target switching block.

In this arrangement, it is possible for the target switching block toperform the same switching-determination process as the first switchingblock because the switching information that is stored in the firstmemory of the first switching block is copied to the second memory ofthe target switching block prior to starting the switching-determinationprocess using the target switching block, after completion of theprocess of setting the determination-operation mode of the targetswitching block.

Although the present invention has been described and illustrated indetail, it is clearly understood that the same is by way of illustrationand example only and is not to be taken by way of limitation, the spiritand scope of the present invention being limited only by the terms ofthe appended claims.

What is claimed is:
 1. A network switching device comprising: aninterface block to be connected to at least one line, that receivespackets and sends packets; a switching block that holds switchinginformation and performs, based on the switching information, switchingprocess of packets sent or received by the interface block and theswitching block is operated by at least one of a plurality of operationmodes with different levels of power consumption while the interfaceblock is operated by a predetermined power consumption.
 2. A networkswitching device according to claim 1, wherein the switching block isadapted to change an operation mode among the operation modes while theinterface block is operated by a predetermined power consumption, wherethe operation modes to be changed are not corresponding to a power-offmode.
 3. A network switching device according to claim 2, furthercomprising a control unit that selects an operation mode for theswitching block.
 4. A network switching device according to claim 3,wherein the control unit monitors performance of at least one of eitherthe switching block or the interface block, and selects the operationmode on a basis of the monitored performance.
 5. A network switchingdevice according to claim 3, wherein the control unit monitors trafficof packets to be transferred by the network switching device, andselects the operation mode on a basis of the monitored traffic.
 6. Anetwork switching device according to claim 3, further comprising amemory that stores time information including a time zone and status oftraffic load, wherein the control unit selects the operating modeaccording to the time information.
 7. A network switching deviceaccording to claim 3, wherein: the switching block includes a firstclock generator that generates a plurality of selectable first clocksignals having different frequencies, and at least one constituentcircuit that operates in synchronization with a selected first clocksignal of the first clock signals, and the control unit controlsoperation of the first clock generator to select a first clock signal ofthe first clock signals, to change the operation mode of the switchingblock.
 8. A network switching device according to claim 3, wherein: theswitching block is operated by a first operation mode with a first levelof power consumption while the interface block is operated by a firstpredetermined power consumption, the switching block is operated by asecond operation mode with a second level of power consumption while theinterface block is operated by a second predetermined power consumption,where the first level of power consumption is higher than the secondlevel of power consumption, the control unit further controls whether atleast two of interface blocks are operated independently from selectingeither the first operation mode and the second operation mode for atleast two of the switching device.
 9. A network switching deviceaccording to claim 1, wherein: the switching block is operated by afirst operation mode with a first level of power consumption while theinterface block is operated by a first predetermined power consumption,the switching block is operated by a second operation mode with a secondlevel of power consumption while the interface block is operated by asecond predetermined power consumption, where the first level of powerconsumption is higher than the second level of power consumption.
 10. Anetwork switching device according to claim 1, further comprising acontrol unit that select either the first operation mode and the secondoperation mode for at least two of the switching device adapted tochange an operation mode among the operation modes while the interfaceblock is operated by a predetermined power consumption.
 11. A networkswitching device according to claim 1, wherein the switching blockincludes: a clock generator that generates a plurality of selectableclock signals having a first frequency and a second frequency; and aconstituent circuit that operates in synchronization with a selectedfirst clock signal of the first clock signals to operate, where thecontrol unit controls operation of the a clock generator to select afirst clock signal of the first clock signals, to change the operationmode of the switching block.
 12. A network switching device comprising:a plurality of interface boards to be connected to at least one line,that receives packets and sends packets, where at least one of theinterface board is operating by predetermined power consumption andother interface board is power-off; a switching board that holdsswitching information and performs, based on the switching information,a switching process of packets sent or received by the interface blockand the switching board is settable to at least one of a plurality ofoperation modes with different levels of power consumption notcorresponding to a power-off mode independently from an operating statusof the interface board.
 13. A network switching device according toclaim 12, further comprising a control board including a control unitconfigured to select an operation mode for the switching block.
 14. Anetwork switching device according to claim 13, wherein the control unitis configured to monitor performance of at least one of either theswitching block or the interface block, and to select an operation modeon a basis of the monitored performance.
 15. A network switching deviceaccording to claim 13, wherein the control unit is configured to monitortraffic of packets to be transferred by the network switching device,and to select an operation mode on a basis of the monitored traffic. 16.A network switching device according to claim 13, wherein the controlboard further includes a memory that stores time information including atime zone and status of traffic load, wherein the control unit isconfigured to select an operating mode according to the timeinformation.
 17. A network switching device according to claim 13,wherein: the switching board includes a first clock generator thatgenerates a plurality of selectable first clock signals having differentfrequencies, and at least one constituent circuit that operates insynchronization with a selected first clock signal of the first clocksignals, and the control unit is configured to control operation of thefirst clock generator to select a first clock signal of the first clocksignals, to change the operation mode of the switching block.
 18. Anetwork switching device according to claim 12, wherein the switchingboard includes a switching-board control unit configured to select anoperation mode for the switching board.
 19. A network switching deviceaccording to claim 18, wherein the switching-board control unit isconfigured to monitor performance of at least one of either theswitching block or the interface block, and to select an operation modeon a basis of the monitored performance.
 20. A network switching deviceaccording to claim 18, wherein: the switching board includes a firstclock generator that generates a plurality of selectable first clocksignals having different frequencies, and at least one constituentcircuit that operates in synchronization with a selected first clocksignal of the first clock signals, and the control unit is configured tocontrol operation of the first clock generator to select a first clocksignal of the first clock signals, to change the operation mode of theswitching board.